While trying Madjik's version of making wings, I enountered this picture:
It appears that the grid underneath was somehow showing up through the picture. Anti-aliasing was off for the sprioshape but not the line. There were three layers: a white background, the spiroshape layer, and the line.
Just a temporary glitch. Didn't go away until I tried again with a new document. For what it's worth... :?